1. Field of the Invention
The present invention relates to a lead frame and a method for producing a surface mount type piezoelectric vibrator using the same, a resin mold construction of a piezoelectric vibrator, a surface mount type piezoelectric vibrator, and an oscillator, an electronic unit and a wave timepiece each having the same.
2. Description of the Related Art
Piezoelectric vibrators are indispensable to the production of industrial products such as watches, oscillators, and electronic units. Piezoelectric vibrators are used as timekeeping sources, timing sources or reference sources for signals. Piezoelectric vibrator packages commonly used include cylinder-type packages. The configuration of a cylinder-type package piezoelectric vibrator will be described below with reference with drawings.
FIG. 31 is an exploded perspective view showing the configuration of a cylinder-type package piezoelectric vibrator. As shown in FIG. 31, a cylinder-type package piezoelectric vibrator 6 has a piezoelectric vibrating piece 4 bonded to an inner lead 2 inside an airtight terminal 1 having two lead terminals. The piezoelectric vibrating piece 4 is made of piezoelectric material such as quartz crystal and formed to be shaped like a tuning fork through photolithography technology. The tuning-fork type piezoelectric vibrating piece 4 is formed with an exciting electrode 4a on the surface of each of two vibrating arm portions thereof. Amount electrode 7 connected to the exciting electrode 4a is formed on the surface of the airtight terminal 1 side of the piezoelectric vibrating piece 4.
The piezoelectric vibrating piece 4 is bonded to the inner lead 2 inside the airtight terminal 1 through the mount electrode 7. The inner lead 2 passes through the airtight terminal 1, serving as an outer lead 3. The inner lead 2 and the outer lead 3 together is referred to as a lead terminal. At the outside perimeter of the airtight terminal 1, the tuning-fork type piezoelectric vibrating piece 4 is covered with a cylindrical bottomed metal sealing tube 5 so that the airtight terminal 1 is airtight sealed to form a vacuum inside.
When predetermined voltage, as drive voltage, is applied to the two outer leads 3, the cylinder-type package piezoelectric vibrator configured as described above permits current to flow from the inner lead 2 through the mount electrode 7 to the exciting electrode 4a. This thus causes the piezoelectric vibrating piece 4 to oscillate at a predetermined frequency.
Unlike other electronic parts, the cylinder-type package piezoelectric vibrator 6 as described above cannot be surface mounted as it is using an automatic mounting machine. The cylinder-type package piezoelectric vibrator 6 is covered with resin to allow surface mounting using an automatic mounting machine. This resin-covered type of cylinder-type package piezoelectric vibrator is known as a surface mount type piezoelectric vibrator.
FIGS. 32 and 33 are views describing a surface mount type piezoelectric vibrator. FIG. 32 is a perspective appearance view of a surface mount type piezoelectric vibrator and FIG. 33 is a schematic cross-sectional view showing the inside construction of a surface mount type piezoelectric vibrator with resin cut off.
As shown in FIGS. 32 and 33, a surface mount type piezoelectric vibrator 31 has a cylinder-type package piezoelectric vibrator 6 provided in the middle. An electrode terminal 33 is provided at the tip side of an outer lead 3 for mounting onto an external substrate. The electrode terminal 33 is formed to extend from a lead frame 60. The electrode terminal 33 is shaped like a crank. One end of the electrode terminal 33 is to be bonded to the outer lead 3 while the other end is to be mounted on a substrate. The electrode terminal 33 is disposed so that the portion that is to be mounted on a substrate is directed outward of the surface mount type piezoelectric vibrator 31.
A surface mount type piezoelectric vibrator 31 manufacturing process includes a process for bonding an outer lead 3 of a vibrator 6 to an electrode terminal 33, a resin mold process for coating the cylinder-type package piezoelectric vibrator 6 with resin, a cutting process for separating a portion connecting a lead frame 20 to a resin mold portion from the lead frame 20, and a process for performing an electrical test on the surface mount type piezoelectric vibrator 31.
[Process for Bonding an Outer Lead to an Electrode Terminal]
In a process for bonding an outer lead to an upper electrode terminal, a vibrator 6 is first carried into each space portion located inside a lead frame through a predetermined transfer tool capable of holding the vibrator 6. The outer lead 3 is brought into contact with and the upper electrode terminal of the electrode terminal 33 and voltage is applied to both, thereby bonding both to each other.
As shown in FIGS. 34 and 35, a lead frame 60 for a conventional surface mount type piezoelectric vibrator has side frames 61 of a carrying and positioning section, section bars 62 and arrangement areas 64 for vibrators 6. These individual components are provided across the width of the lead frame 60 in two rows. Arrangement areas 64 for vibrators 6 are partitioned by a frame 63 for supporting electrode terminals 33 into two rows. Typically, these side frames and sections bars are generically called frame bars.
In the arrangement area 64 for the vibrator 6, a pair of electrode terminals 33 protrude from the side frame 61. A dummy terminal 32 also protrudes from a frame 63 for support the lead frame so that the dummy terminal 32 faces the electrode terminal 33. These terminals, the electrode terminal 33 and the dummy terminal 32, are disposed to face each other across the width of the lead frame 60. As shown in FIG. 35, a plurality of positioning through holes 65 are provided at predetermined intervals in each of the carrying and positioning side frames 61 of the lead frame 60.
The outer lead 3 of the vibrator 6 and the electrode terminal 33 are aligned with the above conventional lead frame 60 for welding purposes in a manner described below. A positioning reference block (not shown) is first prepared. The positioning reference block has a plurality of positioning pins for positioning the lead frame 60 provided to stand up at constant intervals in association with welding positions. The positioning reference block is aligned with the lead frame 60 by inserting the plurality of positioning pins into the plurality of corresponding positioning through holes 65 of the lead frame 60. This causes the outer lead 3 of the vibrator 6 to be aligned with the electrode terminal 33 for welding purposes.
To weld outer leads 3 of the vibrator 6 to electrode terminals 33, vibrators 6 are then disposed in areas 64 in the lead frame 60 provided for arranging plurality of vibrators 6. The outer lead 3 is then placed on the upper electrode terminal 33c of the lead frame 60, as shown in FIG. 37. Welding is performed by placing both the outer lead 3 and the upper electrode terminal 33c between an upper bonding electrode 37 and an lower bonding electrode 36 and applying voltage to the bonding electrodes 36, 37.
[Resin Mold Process]
A conventional resin mold process for a surface mount type piezoelectric vibrator 31 will be described below. A surface mount type piezoelectric vibrator 31 has a sealing tube in the middle thereof. An electrode terminal for mounting on an external substrate is provided on the tip side of an outer lead. The electrode terminal is formed to extend from a lead frame. The electrode terminal is formed like a crank. One end of the electrode terminal is to be bonded to the outer lead 3 while the other end is to be mounted on a substrate. The surface mount type piezoelectric vibrator 31 has the portion to be mounted on a substrate disposed to face outward.
In the resin mold process for the surface mount type piezoelectric vibrator 31, a vibrator 6 is coated with resin mold material at a resin-molded section formed inside a lead frame 60 space. The resin-molded section is formed of molds. The vibrator 6 is held between an upper mold and a lower mold for resin molding.
In a surface mount type package, burs called place thickness burs of a lead frame 60 are produced on the sides of the package and prevent an increase in outside dimensions of the package. In the surface mount type package, as shown in FIGS. 34 to 36, it is known that molds for resin mold are placed in blocks each shaped by a side frame 61 and a section bar 62 formed to surround the outside perimeter of the package and a frame 63 for supporting lead terminals for molding to form the shape of the external sides of each package.
Mold resin material is poured into the molds with a piezoelectric vibrator held between a contact portion formed on the top surface of the lower mold and the inside of the upper mold for molding purposes. This forms surface mount type piezoelectric vibrators 31 each having a resin mold portion as shown in FIG. 32 in arrangement areas 64 of the lead frame 60 for a plurality of vibrators.
[Process for Cutting Electrode Terminal Portions]
In a process for cutting electrode terminal portions, each of the dummy terminals 32 and the electrode terminals 33 connecting to the surface mount type piezoelectric vibrators 31 on the lead frame 60 are cut in predetermined positions. This separates individual surface mount type piezoelectric vibrators 31 from the lead frame 60.
[Electrical Test Process]
An electrical test process for the surface mount type piezoelectric vibrator 31 has required more measurement time in response to measurement items for guaranteeing performance characteristics of the surface mount type piezoelectric vibrator 31 and a measurement accuracy in recent years. Much time is therefore spent on the electrical test.
The electrical test process involves separating individual surface mount type piezoelectric vibrators 31 from the lead frame 60 after resin mold and carrying, positioning and electrically inspecting individual surface mount type piezoelectric vibrator 31 to distinguish between non-defective and defective vibrators. Characteristics of surface mount type piezoelectric vibrators 31 are classified according to users' applications.
Surface mount type piezoelectric vibrators 31 are loaded on tapes and the like according to types such as different load capacity as serial equivalent static capacity and frequency deviation, which completes the surface mount type piezoelectric vibrator 31 manufacturing process.
The longer measurement time is, the more accurate frequency measurements for vibrators 6 will be. The higher the accuracy required is, the longer measuring time will therefore be.
For the electrical test method described above, a method is known which involves bringing electrical contact terminals into contact with the electrode terminals for simultaneous batch electronic part measurement.
The surface mount type piezoelectric vibrator 31 manufacturing method described above, however, has problems in individual manufacturing processes.
[Process for Bonding an Outer Lead to an Electrode Terminal]
The process involves bonding the outer lead 3 of the surface mount type piezoelectric vibrator 31 to the upper electrode terminal 33c by bringing the outer lead 3 into contact with the upper electrode terminal 33c for electrical continuity and applying voltage. The process have problems that will be described below. Particularly such a boding method has problems described below in properly aligning the lead frame 60 with the vibrator 6.
The aforementioned alignment requires the successful alignment of three points, a turning angle difference θ for the outer lead 3, a bonding position for electrical continuity with the outer lead 3, and the position of the cutting end of the outer lead 3.
In other words, as shown in FIGS. 37 and 38, the alignment of these three points include a turning angle difference θ between a pair of two upper electrode terminals 33c and the outer lead 3, the alignment of a bonding point 33d located in the middle of the upper electrode terminal 33c with a required bonding point in the bent outer lead 3, and the handling of the length of the terminal of the outer lead 3 between the upper electrode terminal 33 and the contour of the piezoelectric vibrator. The alignment of these three points will be described below in detail.
1. The length of the part of the outer lead 3 that protrudes from the airtight terminal 1 is smaller than the contour of the sealing tube 5 of the vibrator 6. Even about a few scores of grams of load also result in the plastic deformation of the outer lead 3. Therefore, it is difficult to regulate the turning angle difference θ for the outer lead 3 with an external force. Although, therefore, the turning angle difference θ for the outer lead 3 is regulated with the dead weight of the vibrator 6, the turning angle difference θ is actually too small for alignment and a required positional accuracy is not met in some cases.
2. The bonding point 33d located in the middle of the electrode terminal 33 is coincided with a required bonding point in the bent outer lead 3. In a process for bending the outer lead 3 in advance, misalignment of the turning angle difference θ for the outer lead 3 results in an insufficient bend in the outer lead 3, thus making impossible the alignment of the required bonding point in some cases.
3. As described earlier, even a small load results in the plastic deformation of the outer lead 3. It is therefore difficult to directly regulate the length and position of the terminal of the outer lead 3 with a jig and the like. Thus, conventional positioning means having a radiused (curved) surface corresponding to the cylindrical side of the vibrator 6 is provided for alignment using the shapes of the sealing tube 5 and the airtight terminal 1 in the longitudinal direction of the vibrator 6. In a process for sealing the sealing tube 5 and the airtight terminal 1, however, there is a dimensional deviation in the longitudinal direction of the vibrator 6 with a resultant deviation in the cutting accuracy for the outer lead 3, thus making the above alignment insufficient in some cases.
Particularly machining using a transfer jig will make it impossible to proceed with subsequent processes properly under any of the above-mentioned situations.
In addition, an insufficient alignment of the sealing tube 5 described above can result in warpage in the lead frame 60 in the longitudinal direction thereof because of the contact of the dummy terminal 32 facing the electrode terminal 33 with the sealing tube 5 on the lead frame 60. Any warpage in the lead frame 60 makes it possible to proceed with subsequent processes properly when the lead frame 60 is mechanically carried and aligned.
In the resin molding process that follows the bonding process descried above, an incorrect alignment of the vibrator 6 in molds also results in not only problematic electrode terminal 33 bonding. The incorrect alignment also results the problematic partial exposure of the vibrator 6 from mold resin the resultant incorrect formation of the periphery of the vibrator 6.
[Resin Mold Process]
The resin molding process for a conventional surface mount type piezoelectric vibrator 31 has problematic points as described below.
1. The size and arrangement of a mold 66 for molding the periphery of each of vibrators 6 out of resin in the lead frame 60 are as shown in FIG. 39. The mold 66 is long in the longitudinal direction of the lead frame 60.
Each of the vibrators 6 in the lead frame 60 has the longitudinal side thereof disposed across the width of the lead frame 60 as shown in FIG. 35.
The material of the lead frame 60 is conductive material such as an iron-containing alloy. An iron-containing alloy is also used for molds for resin molding. The lead frame 60 and these molds are made of the same iron-containing materials. However, each of these materials has a different coefficient of linear expansion. In resin molding, the mold 66 for resin molding and the lead frame 60 are heated to temperatures between 150 and 180° C.
The difference in coefficient of linear expansion between the mold 66 for resin molding and the lead frame 60 causes a misalignment between the mold 66 for resin molding and the lead frame 60. The misalignment appears in the longitudinal direction of the lead frame 60 can easily appear across the width of the surface mount type piezoelectric vibrator 31.
The contour of the resin-molded surface mount type piezoelectric vibrator 31 and the shape of the electrode terminal 33 in the lead frame 60 causes misalignment therebetween due to the above-mentioned difference in coefficient of linear expansion from the center of the surface mount type piezoelectric vibrator 31 and across the width thereof. The misalignment results in a difference in size of the electrode terminal 33 across the width of the surface mount type piezoelectric vibrator 31. In the electrode terminal 33 cutting process after the resin molding process, the ends of electrode terminal 33 are cut off from the lead frame 60. The difference in size of the electrode terminal 33 across the width of the surface mount type piezoelectric vibrator 31 can cause contact of a cutting punch with the mold resin thereof, thus resulting in problematic resin chips due to lead cutting. As described above, the resin chipping resulting from resin molding has an adverse influence on the product performance of the surface mount type piezoelectric vibrator 31.
2. The electrical test process for the surface mount type piezoelectric vibrator 31 have required more measurement time because of measurement items for guaranteeing performance characteristics of the surface mount type piezoelectric vibrator 31 and a measurement accuracy in recent years. Much time is therefore spent on the electrical test. Individual surface mount type piezoelectric vibrators 31 are problematically difficult to handle so as to guarantee the performance characteristics thereof.
To ensure the characteristics and reliability of the surface mount type piezoelectric vibrator 31, a resin mold construction is therefore required for the surface mount type piezoelectric vibrator 31. The resin mold construction would allow measurements of the surface mount type piezoelectric vibrator 31 on the lead frame 60 in the electric test and the simultaneous quick batch measurements of more surface mount type piezoelectric vibrators 31. The time reduction would enable resulting saved time to be allocated to measurements for performance characteristic measurement items for measurement accuracy guarantee, thus making it possible to ensure a higher reliability and a higher quality.
3. For the above purpose, a higher cavity density is required for the resin mold construction, which would allow electrical tests performed on the lead frame 60 and allow for the layout of the lead frame 60 for simultaneous batch contact of more electrode terminals. However, the higher cavity density would result in a problematically complicate mold for the resin mold construction.
In other words, contact surface of the mold are inserted between the resultant outer peripheral portion of the above-mentioned resin mold construction to be shaped to enclose the vibrator 6 and the side of the vibrator 6. The outer peripheral portion shaped to enclose the vibrator 6 to support the positional accuracy of a terminal formation portion is to be disposed on the side of the vibrator 6 as a frame 63 for supporting the section bar 62 and the lead terminal. In the mold 66 for forming cavities, therefore contact surfaces between the outer peripheral portion to be shaped to enclose the vibrator 6 and the side of the vibrator 6 and between a section bar 62 and the mold 66 are formed for each cavity. Resin burrs resulting from resin molding include thin burrs produced on the sides of the package and the top surface of the lead frame from a mold clamping clearance between the upper mold and lower mold. To allow the removal of these thin burrs, a mold clamping clearance accuracy is required, as far as thin burrs can be removed, in a position where the contour of the package is to be shaped and in positions of section bars 62. To make a plurality of adjacent cavities closer to one another for a higher cavity density, a sufficient strength is therefore required for narrower section bars 62 and the mold. The mold must also be of a complicated shape that would avoid the shape of section bars 62 together with the maintenance of the accuracy of individual mold clamping clearances.
[Process for Cutting Electrode Terminal Portions]
In the process for cutting electrode terminal portions of the surface mount type piezoelectric vibrator 31, a notch groove is sometime formed in advance in each cutting point in advance for cutting load reduction. As an adverse influence of this, warpage in the lead frame 60 sometimes results. In other words, the formation of notch grooves in the lead frame 60 can lead to the expansion of notch groove formation surfaces, thus resulting in warpage in these surfaces. Any warpage in the lead frame 60 will make it impossible to proceed with subsequent processes properly when the lead frame is mechanically carried and aligned.
[Electrical Test Process]
The electrical test process for the surface mount type piezoelectric vibrator 31 suffer from problems described below. Particularly the back measurement of surface mount type piezoelectric vibrators 31 each having the electrode terminal 33 in contact with the outer lead 3 for electrical continuity suffers from problems described below.
1. A limited number of electronic parts are measured all together in the electrical test method that involves bringing electrical contact terminals into contact with electronic parts mounted in a row on the side frame at a right angle.
2. As shown in FIGS. 35 and 36, on a conventional lead frame 60, piezoelectric vibrators 6 are mounted in two rows at a right angle to the longitudinal direction of two side frames 61 (in the vertical direction in FIG. 35). This requires section bars 62 bridging between the side frames 61 or the frame 63 for supporting lead terminals, and the like. As shown in FIG. 35, there is a limit to the arrangement of piezoelectric vibrators 6 at shorter intervals for a higher density and a limited number of piezoelectric vibrators 6 are measured all together.
3. If, on the other hand, a plurality of surface mount type piezoelectric vibrators 31 are arranged at shorter intervals for a high density and driven to oscillate, the oscillating condition of adjacent surface mount type piezoelectric vibrators 31 and their intervals can affect their oscillation frequency.
FIG. 40 is a diagram showing the oscillation circuit of a common piezoelectric vibrator. CS, represented by a dashed line, refers to stray capacity. FIG. 41 is a graph showing a relation between the load capacity of a common piezoelectric vibrator and frequency deviation. The axis of abscissas CGOUT shows a load capacity while the axis of ordinates shows frequency deviation. It is well known that the oscillation frequency varies with the magnitude of the capacitor CG in FIG. 40, as in the graph shown in FIG. 41. It is also well known that the stray capacity is proportional to the area of wiring connected with the oscillation circuit and inversely proportional to the distance.
It is known from the above fact that the frequency of piezoelectric vibrators 6 also vary between adjacent surface mount type piezoelectric vibrators 31 to be measured in the electrical test process for surface mount type piezoelectric vibrators 31. The distance between adjacent surface mount type piezoelectric vibrators 31 has a different influence on the frequency of the surface mount type piezoelectric vibrator 31. If an attempt is made to meet the necessity of enhancing the layout density of the lead frame relative to the lead frame 60 on which more electrical contact terminals are brought into contact with electronic parts as described above, piezoelectric vibrators 6 can be affected by the influence of the frequencies of piezoelectric vibrators 6 oscillating each other due to the distance between adjacent surface mount type piezoelectric vibrators 31, thus making it difficult to make correct frequency measurements.
The problems described above are aggregately caused by the lead frame 60, which constrains requirements in the surface mount type piezoelectric vibrator 31 manufacturing process.